How to identify ancient KornShell version

We had a guy retire on us, and the documentation left behind is a little on the light side. Need a little help identifying and using part an older client-server system.

The server itself is maintained by several excellent Unix admins. We are currently running AIX 7.1.0.0 on the server side.

However, when we log in using the proprietary SSH client, we are greeted with a shell that looks familiar, but is strange in other ways. The shell itself seems to be KornShell:

echo $0
-ksh

But the shell doesn't respond to normal shell commands (cannot tap up/down to recall recent commands, cannot backspace normally, no auto-complete with tab, etc.)

Recent commands are recalled using ESC + k

If the ESC key is tapped, the terminal stops responding to input until i, a, s, or cc are pressed (or k, as already mentioned brings up the most recent command).

To edit a recalled command we have to tap SHIFT + UP

Backspace is actually the RIGHT arrow, and to clear a typed command we have to hit SHIFT + RIGHT

The whence command is not available, and none of the techniques to discover the KSH version on this page worked.

Someone in our office suggested this is some kind of inline vi.

Does anyone else have any advice? Is there any documentation available?